1. Field of the Invention
The present invention relates generally to tube quality inspection and, more particularly, is concerned with an improved tube drive apparatus employing radially oriented flexible drive belts being arranged to drivingly engage a tube so as to axially rotate and/or longitudinally move it along a path past an ultrasonic inspection device.
2. Description of the Prior Art
Because of their critical roles as fuel, control and instrumentation rods in nuclear reactors, tubes composed of zirconium and other materials must meet very stringent quality control standards. Ultrasonic testing is one common method used to identify material flaws or unacceptable dimension deviations in the tubes.
One conventional tube inspection technique involves moving a tube past an ultrasonic testing device. The testing device includes an ultrasonic source with transducers located adjacent the moving tube which are capable of transmitting an ultrasonic signal toward the moving tube and receiving an echo from the tube, and then analyzing it to determine the acceptability of the tube. The ultrasonic source is capable of transmitting pulses in the megahertz range and so to effectively take advantage of this the tube is moved longitudinally past the ultrasonic source and sometimes simultaneously rotated axially which causes the pulses to strike along a helical pattern or path around the tube resulting in a maximum number of meaningful data points.
One conventional drive apparatus which is used for moving tubes in the helical path past the ultrasonic testing device employs an arrangement of three rotating rollers positioned radially with respect to the axis or centerline of the tube at approximately 120 degree intervals from one another around the circumference of the tube. The rollers are angularly oriented with respect to the tube centerline to produce simultaneously longitudinal movement and axial rotation of the tube. Each of the rollers has a polyurethane rim which engages the tube. The rim is mounted on a steel wheel that is driven through a steel-core belt. Each roller is driven via the steel-core belt by a drive wheel and the shaft of the roller can be inclined to that of the drive wheel to adjust the longitudinal movement and axial rotation of the tube.
With such an arrangement, if the rim of a roller develops a flat spot from friction caused by improper alignment or a temporary binding condition, then every revolution of the roller will impart a load which can possibly dent the tube and the smooth motion of the tube will be interrupted causing difficulty in synchronizing the ultrasonic source with the passing tube. Furthermore, the steel-core belt which drives each roller, although very durable, is sufficiently rigid as to restrict the range of the angle at which the roller shaft can be oriented relative to the tube centerline to approximately ten degrees. There also exists a need to measure wall thickness variations in an axial direction which will indicate the pitch of any spiral that may have developed in the tube during the pilger forming process.
Consequently, a need exists for improvements in the tube drive apparatus so as to avoid the problems and limitations of the conventional drive arrangement used heretofore.